None.
Not applicable.
Not applicable.
1. Field of the Invention
The present invention relates generally to a method and apparatus for grounding circuit boards in electronic devices, and more particularly relates to a method and apparatus for electrically grounding a processor board, such as a printed circuit board, to a chassis.
2. Description of the Related Art
Processor boards, such as printed circuit boards (xe2x80x9cPCBxe2x80x9d) with components mounted thereon referred to as printed circuit assembly or xe2x80x9cPCAxe2x80x9d, are mounted to the chassis of various electronic devices. The mounting of the processor board or PCA to the chassis typically provides needed electrical grounding of the board to the chassis. For example, a server computer uses a processor PCA that requires a grounding means to meet agency EMC compliance. Oftentimes, it is necessary to electrically ground a printed circuit board at several distinct locations on the board. A printed circuit board may include several conductor layers separated by insulator layers. The various conductor layers are electrically connected by vias, or electrical connector barrels, typically of copper, formed in the circuit board through the layers of conductors and insulation. Electrical grounding of these intermediate conductor layers can be accomplished with vias extending through the board to its upper and lower surfaces.
One prior method for PCA mounting and electrical grounding required the use of xe2x80x9cblunt nosexe2x80x9d standoffs with a companion screw inserted through a hole in the PCA and threaded into the standoff. The standoff and screw were made of electrically conductive materials. The hole in the PCA typically included a grounding pad around the hole on the upper and lower surfaces of the PCB. Thus, electrical grounding was provided to the portion of the PCA in electrical contact with the screw and standoff. However, some system processor boards are quite large and complex and may require for example fifteen or eighteen standoffs. The more screws required, the more time involved in installing and removing the board and also the increased risk of damaging the PCA, as for example, by the air driver bit slipping off the screw head and damaging components on the board. This prior PCA mounting method is labor intensive, but provides effective electrical grounding and securement to the chassis.
Another method currently in use for mounting the PCA involves the usage of xe2x80x9cbullet nosexe2x80x9d standoffs or mounting studs. The bullet nose mounting studs are attached to the chassis, as for example by pressing them into the chassis. The mounting stud was made of electrically conductive material. A typical bullet nose mounting stud includes a cylindrical base which sharply transitions at an upper base face to a reduced diameter cylindrical stem. The cylindrical stem transitions to an enlarged diameter nose at a lower nose face. The nose has an upper portion generally rounded in shape like a bullet. The diameter of the base portion is greater than the diameter of the nose which is greater than the diameter of the stem for reasons which are explained below.
The PCB includes a keyhole-shaped opening having a generally enlarged circular area connected to a smaller throat area. The enlarged circular area is larger in diameter than the mounting stud nose but smaller in diameter than the upper base face to allow the enlarged circular area of the PCB opening to be lowered over the nose and onto the upper base face. With all of the PCB openings positioned onto the mounting studs, the PCB is slid such that the mounting stud stems are received in the smaller throat area of the keyhole-shaped openings. Typically, the height of the stem (which is the distance between the upper base face and the lower nose face) is slightly greater than the thickness of PCB to permit sliding action and also to allow for manufacturing tolerances. The width of the throat area is less than the diameter of the lower nose face such that the PCB is restrained in the direction of the longitudinal axis of the mounting stud between the lower nose face and the upper base face. A grounding pad was included around the end of the throat area on the upper and lower surfaces of the PCB to provide electrical grounding by contact with the mounting stud.
The xe2x80x9cbullet nosexe2x80x9d mounting studs for PCA mounting do not effectively provide continuous electrical grounding of the PCA to the system chassis. This is due primarily to manufacturing tolerances involved in the manufacture of the PCB and the mounting studs. Additionally, it is necessary to have some xe2x80x9cplayxe2x80x9d in order to be able to slide the PCB into the throat area. Furthermore, typically a few of the mounting studs are replaced with blunt nose standoffs with a companion screw and a round hole rather than the keyhole-shaped opening to secure the PCA and provide continuous electrical grounding. The use of screws again increases the time and risk of damage as explained above.
It is desirable to have an electrical grounding device for continuously grounding a processor board to a chassis using standard bullet nose mounting studs and keyhole-shaped openings. It is also desirable that any new electrical grounding device for use with bullet nose mounting studs be cost sensitive, easily manufactured, highly reliable, and designed for mass production.
The present invention is an electrical ground clip for grounding a processor board to a chassis using standard bullet nose mounting studs and keyhole-shaped openings. The ground clip of the present invention is cost sensitive, easily manufactured, highly reliable, and designed for mass production.
One embodiment of the ground clip of the present invention includes a generally circular-shaped upper body portion, and a lower portion with a number of contiguously attached, peripherally spaced retentive leads. The upper body portion contains a peripheral side opening opposite the peripherally spaced retentive leads. Upper body ends at the side opening are formed outwardly at an angle to receive a bullet nose mounting stud or standoff attached to a chassis. The inner diameter of the ground clip""s circular-shaped upper body portion is smaller than the diameter of the nose of the mounting stud. The retentive leads of the ground clip""s lower portion are inserted through corresponding holes in grounding pads located at one end of a keyhole-shaped opening in a processor PCB. The retentive leads are soldered by conventional means to the PCB to ensure electrical contact of the ground clip to the PCB.
The PCA contains keyhole-shaped openings and is installed over the bullet nose mounting studs. Initially, the PCB is positioned over the nose of the mounting studs and brought into contact with the upper base face of the mounting stud. As the PCB is slid towards its final position, the upper and lower surfaces of the PCB are loosely captured by the upper base face and the lower nose face of the mounting stud. The mounting stud stem is smaller in diameter than the upper base face and lower nose face, and smaller than the throat area of the keyhole-shaped opening in the PCB. As the PCB reaches its final position, the upper body portion of the ground clip engages the nose of the mounting stud, springs open, then returns to a position that partially surrounds and makes firm contact with the nose of the mounting stud. The firm contact of the ground clip around the mounting stud nose provides continuous electrical grounding.
The ground clip of the present invention is compatible with existing components and mounting techniques. The present invention is soldered to the processor board and electrically grounds the processor board to the chassis via the bullet nose mounting studs used to secure the processor board to the server chassis. The ground clip can be manufactured at low cost and be easily implemented. In addition to providing consistent electrical grounding of the processor board to the chassis, it also includes the benefits of easier and quicker installation of the processor board to the chassis. The ground clip of the present invention can be installed by conventional means by the manufacturer of the PCA. The present invention eliminates the risk of damage to the PCA caused by an air driver bit slipping off a screw head and damaging components on the board.